Analysis of the spatial-temporal variation of water quality in Jinxi River, a tributary of Southern Tiaoxi River
南苕溪支流锦溪水质时空变化特征分析

Grey clustering,comprehensive pollution index(CPI) and hierarchical clustering methods were employed to investigate the recent spatial-temporal variation of water quality in Jinxi River,a tributary of Southern Tiaoxi River.The results show that the water quality at the estuary section,where Jinxi River flows into Qingshan Reservoir,was gradually improved from 2005 to 2009 and could reach the Grade Ⅲ of the water standards since 2007 in the grey clustering analysis.The CPIs in autumn and winter were higher than those in spring and summer during the studied period from the autumn of 2009 to the summer of 2010.The highest CPI was observed in dry season while the highest sub-indexes of TN and TP appeared in the wet season,implying that non-point source pollution had already accounted for a significant portion of the overall pollution.In terms of spatial variation the CPI of Jinxi River aggravated gradually from Linglong Bridge to Jiang Bridge where it reached a maximal value of 13.25,and then mitigated to some extent till Sanyan Bridge.According to the hierarchical clustering analysis,Jinxi River could be divided into three segments,i.e.,the light-pollution(from Linglong Bridge to Dongyun Bridge),heavy-pollution(from Qunli Bridge to Jiang Bridge) and moderate-pollution segment(from Jiang Bridge to Sanyan Bridge).The COD,TN and TP from the upstream of Jinxi River contributed to 65%,54% and 49% of their total loadings,respectively.Therefore,the agricultural non-point source has become the restrictive factor for water quality improvement in Jinxi River.